This laboratory studies the role of the skin as an immunological organ. We study the mechanisms involved in delayed type hypersensitivity (DTH) reactions in the skin and use this knowledge to better understand lymphocyte- mediated skin diseases. In the past year we have continued to focus our studies on 1) the immune elements of the epidermis and dermis and on their interactions with the rest of the immune system, 2) the development of a model that may provide insight into mechanisms involved in autoimmune reactions in skin and in the maintainance of tolerance to epidermally-derived proteins and 3) the identification of the specific precursors of Langerhans cells. We have attempted to delineate whether and how CD4+ T cell responses could be skewed toward Th1 or Th2 rich reactions. We found that a relative skewing of a T cell response can occur as a consequence of immunization with various types of adjuvants. We also continue to try to skew these inflammatory responses using gene transfer into bone marrow derived dendritic cells (BMDC). In this regard, we have characterized the ability of antigen-pulsed BMDC to induce various types of DTH reactions and are now attempting to utilize these cells as vehicles for gene vaccination experiments. We have also completed a study that demonstrates that LC express FasL after activation triggered through CD40 molecules on their surface, but not by stimulation with LPS or IFNg. These studies suggest a new feedback mechanism to downregulate T cell activation by LC through the interaction of the TNF receptor/ligand superfamily, CD40/CD40L and Fas/FasL. The second project that we are pursuing involves the development of a model of skin autoimmunity and tolerance induction. We are crossing mice that have a TCR transgene that recognizes ovalbumin in association with H-2b (OT-I) with mice that have been generated with a K14-ovalbumin (K-14 OVA) encoding gene. These mice have the TCR for ovalbumin and express ovalbumin in the epidermis but have no apparent disease. Preliminary studies indicate that these mice are depleted of CD8 cells that have the TCR transcripts. We are also using the K-14 OVA mice as targets for immunological reactions in the skin. We are currently injecting T cells from OT-I mice and assessing their role in causing inflammatory skin lesions. We have now also begun breeding OT-II mice (that have a TCR that recognizes OVA paptides in Class II MHC molecules) and will characterize any abnormalities that occur when cells from these mice are infused into the K-14 OVA mice. Finally, we are trying to identify the specific precursors of Langerhans cells. To do this we are using X-irradiated bone marrow reconstituted mice and using A X B donors into A recipients. We are using various cell populations that are presorted to determine which ends up being a Langerhans cell. Furthermore, we are able to accelerate the repopulation of Langerhans cells in skin by using topical agents that promote the egress of host Langerhans cells from the skin.